Silane compounds are used to improve adhesion between polymeric materials and substrates such as organic materials (e.g., hydrocarbon-based polymeric materials), and inorganic materials, including metals, fiberglass and glass (see for example, "A Guide to Dow Corning Silane Coupling Agents", Form No. 23-012B-85, published by Dow Corning Corporation, Midland, Mich.). In some applications, compositions comprising silane compounds are hydrolyzed to their silanol form, which may then react with the substrate, e.g., by reacting with hydroxyl moieties present in an inorganic material. The silane compound can also include an organofunctional group that reacts with the substrate to enhance the bond strength between the substrate and the silane. Compositions comprising silane compounds have been successfully used as adhesion promoters with some fluoropolymers, see for example, "`Dynamar` Bond Metal Bonding Agent--5150", Brochure No. Y-IFE5150-2 (73.05)RI, published by the 3M Company, 1983.
Past silane-containing aqueous bonding compositions have generally included an organic solvent component. Although these bonding compositions have also contained minor amounts of water to hydrolyze the silane compound, a major portion of these bonding compositions has been organic solvent. Organic solvent is useful within a bonding composition because, among other reasons, organic solvents generally have low surface tensions, allowing good wetting of a substrate. Recently, the use of organic solvents in industry has become disfavored due to their harmful environmental effects, and because of health and safety concerns. Industry has made concerted efforts to eliminate solvent-based coatings and compositions, and replace them with aqueous formulations. What is needed but not provided by the prior art is an aqueous bonding composition that effectively bonds a fluoropolymer to a substrate.